Submerged arc welding (SAW) is a process in which joining of metal pieces is accomplished by heating the metal pieces with an arc existing between an electrode and the metal. In the submerged arc welding process the arc and the molten metal are shielded from the atmospheric oxygen and nitrogen by a blanket of fusible granular flux, which covers the arc. The welding electrode of the submerged arc welding process is a consumable wire electrode continuously fed to the welding process. The flux covering the arc significantly reduces spatter, smoke, and arc flashes, allowing higher utilization the wire electrode at higher welding speeds and deposition rates.
The consumable wire electrodes used in the SAW process are predominantly solid carbon or low alloy steel electrodes, where a specific combination of the wire/flux composition is required for the optimal performance and weld quality. Most of the oxides and compounds incorporated into the flux cannot be added during the steelmaking process because of the differences in the melting temperatures and the problem with their solubility in steel. The resulting metal would have gross inclusions and be very weak. The solution to the problem is to use tubular wire electrodes consisting of a mild steel sheath and a core composition comprising desired elements and compounds in the powdered form. Such a design allows the weld deposits to have the required chemistry without impeding the manufacturing of the consumable electrodes. Tubular electrodes, such as metal-cored and flux-cored electrodes, have also been used in SAW for specialty alloys that are too difficult to draw as a solid wire to the size which is appropriate for the SAW process. For example, hard surfacing applications require the addition of special elements for wear resistance and impact abrasion. Nevertheless, it is attractive to use tubular electrodes in the SAW process to increase the welding deposition rates and control the weld chemistry by selecting the appropriate chemistry of the wire electrode.
The main ingredients in both metal-cored and flux-cored wires are powdered ferro-alloys. In addition, flux-cored electrodes contain non-metallic compounds to help stabilize the arc and create a desired molten slag composition with such physical properties that allow the molted slag to protect the molten weld metal from various undesirable reagents in the atmosphere. Metal-cored wires typically have no more that 5% of non-metallic compounds and metal oxide powder additions in the core (fill percentage) to help stabilize the arc. Flux-cored electrodes are designed to have non-metallic and metallic oxide ingredients of approximately 20-30% by weight to create the physical slag of desired properties during the welding process.
Currently the solid wires used in the SAW process work with the granular flux, yielding up to 99% deposition efficiency. The performance of such welding process is determined mostly by the composition of the granular flux, and much less so by the composition of the wire electrode. Currently, almost 100% of the structural steel market (carbon and HSLA steels) use solid wires When using flux-cored wire electrodes for SAW, deposition efficiency falls down to about 80%. Welding performance in that case is determined by both the fluxed core of the wire and the granular flux, which turns out to be less efficient.